title: Continuous determination of extracellular space and changes of K+, Na+, Ca2+, and H+ during global ischaemia in isolated rat hearts.
abstract: Isolated rat hearts were perfused according to the Langendorff technique and prepared to allow the measurement of left ventricular pressure (LVP), the first derivative of LVP (dP/dt), coronary perfusion pressure (CPP) and heart rate (HR). The hearts were perfused with a modified Krebs-Henseleit solution (KHS; control group) or KHS containing tetramethylammonium-chloride (TMA; 100 microM), which did not influence heart haemodynamics or extracellular potassium accumulation during global ischaemia (GI). TMA was used as a marker to determine changes in the size of the extracellular space (ECS) during 60 min of GI. Extracellular concentrations of K+, Na+, Ca2+, H+ and TMA were measured using double-barreled polyvinyl chloride (PVC) mini-electrodes. Relative changes in the ECS size and net cation movements were calculated from the extracellular TMA and cation concentrations. After 60 min of GI ECS decreased by 74% due to a water shift into the intracellular space (ICS). Within 10 s after the onset of GI extracellular potassium concentration increased in a typical triphasic pattern. A biphasic net efflux of K+ was maximal 2 and 15 min after the onset of ischaemia interrupted by a maximal uptake after 7 min, probably due to the stimulation of the Na+/K+ ATPase. The changes in extracellular sodium and calcium concentrations were biphasic; showing an initial increase occurring approximately during the first 20 min after the onset of GI followed by a decrease. Despite the initial increase of extracellular Na+ and Ca2+ maximal net influx of Na+ and Ca2+ were calculated after 2 and 19 min of GI. Accumulation of H+ in the extracellular space occurred mainly during the first 20 min of GI. It is concluded that, (1) TMA is a useful marker for continuous measurement of changes in the size of the ECS during GI; (2) Changes in extracellular ion concentration are influenced markedly by a water shift from the ECS into the ICS; (3) Stimulation of the Na+/K+ pump causes a transient net uptake of K+ and reduces the net influx of Na+; (4) Ca2+ uptake is decreased transiently probably by increased Ca2(+)-ATPase activity; (5) Energy dependent protective mechanisms for the maintainance of intracellular ionic homeostasis are exhausted after approximately 15 to 20 min of GI in isolated working rat hearts.
authors.affiliation: Institute of Vegetative Physiology, University of Cologne, West Germany.
authors.forename: H
authors.initials: H
authors.lastname: Knopf
authors.forename: R
authors.initials: R
authors.lastname: Theising
authors.forename: C H
authors.initials: CH
authors.lastname: Moon
authors.forename: H
authors.initials: H
authors.lastname: Hirche
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D003327:Coronary Disease / Q000378:metabolism*; D004573:Electrolytes / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism; D066298:In Vitro Techniques; D010477:Perfusion; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism
chemical_list: D004573:Electrolytes; D006859:Hydrogen; D012964:Sodium; D011188:Potassium; D002118:Calcium